and then the ability to make
ShellCommand?(workdir = w2, command = "xxx %s" % w1" )

so that build step scripts can work across repository boundaries.

Currently, I am working these limitations around by using git submodules, which scripts will automatically update, since git has no means to track branches of other repos as submodules.

To me, it would be cleaner, if these cross-repo scripts and builders were possible. Right now, I don't have an urgent need, as I believe submodules are workable, with the noise that the automatic submodule updates bring, it's not an optimal solution, and bears no flexibility. I cannot e.g. override from the outside the commit id values for these submodules.